The acidic hydrolysis of vegetable substrates having a high cellulose and hemicellulose content in view, either of obtaining sugars as such, or of converting thereafter the sweetened liquors into various products such as ethyl alcohol, mixtures of acetone with butyl alcohol and isopropyl alcohol, yeasts for use as protein source, etc . . . has long been known.
However sufficient hydrolysis of the cellulosic substrates is only obtained when using high concentrations of acid and operating at high temperatures, which results in partial sugar destruction, high power requirements and use of expensive materials resistant to these severe conditions. For this reason other hydrolysis methods have more recently been sought, in particular methods operated with cellulase preparations (see, for example, U.S. Pat. No. 3,642,580 and European Pat. No. 0 011 767) which can be used at low temperature and have the advantage of avoiding sugar destruction.
However enzymatic hydrolysis is relatively slow and various treatments have been proposed to accelerate the conversion to sugars, such as mechanical treatments (U.S. Pat. No. 3,642,580) or alkaline treatments (French Pat. Nos. 2 359 206 and 2 327 315). The mechanical treatment has the disadvantage of a high power consumption while the alkaline treatment leads to soluble constituents liable to detrimentally affect the desired subsequent conversions and to pollute the residual liquors.
The object of the present invention is to provide a process for manufacturing sweetened liquors and resultant products from cellulose-containing vegetable substrates, which process does not suffer from the disadvantages of the known processes. This process substantially solves the problems linked to the use of the known severe acid treatment: sugar degradation, corrosion of apparatus, difficulty in disposing of acid solutions after use thereof. The new process also avoids the disadvantages of the conventional enzymatic treatment: insufficient yield, slow conversion.